Early works experimentally demonstrated that aggregate statistics of data, means and correlations respectively could be perceived with high accuracy and compared across classes by humans from data visualizations [1]}, [2]}.
Subsequent analysis of chart perception through extensive human studies found that both individual features as well as aggregate of data could be inferred from good visualizations  [3]}. They varied the number of columns and the entropy of data, showing that for a small number of columns humans can perceive differences and even individual values of aggregates like averages with low error rates.
